Gas. A general term applied to all aeriform or permanently elastic fluids, excepting the compound of oxygen and nitrogen constituting the atmosphere, which is distinguished from the other gaseous bodies by the name of air. (See No. 4072 (Air).) Gases for chemical purposes arc usually generated in a bottle of glass or other appropriate material; or, where the application of heat is necessary, in a retort. A connecting tube of convenient shape is fitted air-tight into the neck or beak of the generating vessels, through which the gas is led into receiving vessels. These are usually bottles, with accurately fitting stoppers.

4031. Pneumatic Trough

4031.    Pneumatic Trough. A vessel or tank nearly filled with water, provided with a shelf placed 1 or 2 inches below the surface. The receiving bottles are first immersed in and filled with the water and then placed neck downwards on the shelf, which is furnished with holes to allow of the passage of the gas into the receivers' from the connecting tube, the end of which is brought immediately under one of the holes. For gases which are easily absorbed by water, mercury or some other fluid is necessary in place of the water. As the gas ascends into the receiving bottle, the water is displaced; when full, and the gas begins to escape, the bottle should be closed with a greased stopper, and removed from the trough.

4032. To Find the Weight of a Gas

4032.    To Find the Weight of a Gas. Multiply the specific gravity of the gas by 3091/2 (the weight in grains of 1000 cubic inches of air), the product will be the weight of 1000 cubic inches of the gas.

4033. To Prevent the Escape of Gas from India-Rubber Tubing

4033.    To Prevent the Escape of Gas from India-Rubber Tubing. India-rubber tubing is slightly permeable to gas. The amount which escapes through the walls of the tube is very small; but it may be advisable sometimes to render an escape impossible. This can be done by giving the tubing a thin coating of a varnish made by dissolving l1/2 parts molasses and 2 parts gum-arabic in 7 parts of white wine and 31/2 parts strong alcohol. The molasses and gum must first be dissolved in the white wine, and the alcohol must be added very slowly, constantly stirring the mixture, or the gum will be thrown down.

4034. Oxygen

4034.      Oxygen. An elementary gas, colorless, tasteless, odorless, and incombustible, having a specific gravity of about 1.057. Oxygen enters largely into the composition of all nature; being a constituent part of the atmosphere (see No. 4072 (Air)), upon which it confers the power of supporting life and combustion; and water, present more or less through the whole world, contains about 88 per cent, by weight, or 33 per cent, by volume, of oxygen; it constitutes also a portion of the majority of the mineral bodies that form the bulk of our globe. It is a powerful supporter of combustion, and its presence is essential to the existence of animal and vegetable life. Oxygen unites with certain other bodies in fixed proportions to form a class of acids distinguished as oxygen acids or oxacids. (See No. 3853.)